Vanillin is also referred to as vanilla aldehyde. The molecular weight of vanillin is 152.14. The common form of vanillin is crystal with white to light yellow color. Vanillin has the melting point of 81° C. and the boiling point of vanillin ranges from 284° C. to 285° C. The specific gravity of vanillin is 1.060.
The flash point of vanillin is 147° C. and the solubility of vanillin is 10 g/L (25° C.) Vanillin is soluble in ethanol and other organic solvents. Vanillin can be found in Peruvian balsam, tallow, vanilla, coffee, grape and brandy. Vanillin smells like vanilla and sweet.
Vanillin is not only an important spice but also an important chemical raw material and an important pharmaceutical intermediate. In the food field, because Vanillin has the aroma of vanilla bean, Vanillin is used as a fixative in various kinds of food. In medicine, vanillin is the raw material for synthesizing medicine intermediates. Vanillin is used to produce drugs commonly used for treating high blood pressure, heart diseases and skin diseases.
1. Chemical Synthesis
1) Lignin method: lignin is widely found in wood and pulp waste. Using lignin as raw material by hydrolysis and oxidation in alkaline medium and so on, vanillin is obtained. Although via the lignin method the cost of the raw materials is low, the yield and quality of vanillin is also low. The lignin method produces vanillin that generally is not used in the food and pharmaceutical industry.
2) Eugenol method: eugenol is the main component of clove oil. In the eugenol method, eugenol is oxidized to obtain the vanillin.
3) Guaiacol method: there are several routes for producing vanillin by guaiacol synthesis. The highest yield of vanillin via guaiacol method reaches 60%. The yield of vanillin by the guaiacol method is usually less than 60%. The guaiacol method is the main production method of vanillin in China.
4) P-hydroxy benzaldehyde, nitrotoluene and p-cresol method: for various reasons, these three methods have not yet been industrialized. The p-hydroxy benzaldehyde method is due to the high price of raw materials. The p-cresol method has strict reaction conditions and low yield. The nitrotoluene method needs large equipment.
5) Safrole method: Safrole is mainly extracted from the camphor oil. The safrole method has long reaction route. The by-products from the safrole method are difficult to separate.
2. Plant Extraction
In the plant extraction, vanillin is mainly extracted vanillin from vanilla beans, but due to the planting of the vanilla beans is restricted by geographical conditions and the vanillin content in the vanilla beans is low, the vanillin extracted from the vanilla beans had low yield and dose not meet the demand of the market. Vanillin produced via the plant extraction is difficult to be accepted by average consumers because of the high price.
3. Biological Transformation Method
The biological transformation method mainly includes plant cell culture method and microorganism transformation method. The cultivation of plant cell culture has relatively long culture period and low yield. The plant cell culture method is not beneficial for industrialization. There are a variety of microorganisms capable of transforming anacylic acid or iso-eugenol to vanillin. The microorganism transformation method takes advantage of short producing period, high yield and low pollution. The microorganism transformation method is beneficial to industrial production.
4. Enzymatic
It has now been found that the eugenol or isoeugenol can be converted into vanillin by the catalysis of lipid oxygenase. The catalytic reaction of lipid oxygenase is mild and the product of lipid oxygenase is easy to purify. However the separation, directed evolution and modification of lipid oxygenase need further study, and the enzymatic method is still in research phase.
In conclusion the aforementioned methods all have some kind of shortcomings.